The need for effective and economical preservative compositions is well known. There are a wide variety of applications where inhibiting the growth of microorganisms is necessary, as for example personal care products such as shampoos, creams, lotions, cosmetics, soaps and household products such as laundry detergents, hard surface cleaners, and fabric softeners. The shelf life of these preparations depends on their resistance to microbial spoilage.
In addition, in many industrial applications, antimicrobial agents are useful in paint, wood, textiles, adhesives, sealants, leather, rope, paper pump, plastics, fuel, oil, and rubber and metal working fluids. The control of slime-producing bacteria and fungi in pump and paper mills and cooling towers is a matter of substantial commercial importance.
Certain compounds have long been known to be useful as preservatives. For example, U.S. Pat. No. 3,987,184 shows the use of 1,3-dimethylol-5,5-dimethylhydantoin (DMDMH) as a useful formaldehyde donor for the preservation of personal care products, cosmetics, and household and industrial products. While it is inexpensive and effective against a wide variety of bacteria, the rate of kill is slow in inhibiting fungi and yeasts.
On the other hand, compounds such as the halopropynyl carbamates are known for their fungicidal activity; however, they are extremely costly and, as a result, have only found applications in specialty areas where high costs can be justified.
Other commercially known preservatives include Quaternium-15 (Dowicil 200, a trademark of Dow Chemical Company). It has the disadvantage of being a solid product which must be solubilized in water before it can be used in the end product. In aqueous solution it exhibits pH drift and causes formulation problems, particularly with regard to viscosity and color.
Imidazolidinyl urea (Germall 115, a trademark of Sutton Laboratories) has virtually no fungicidal activity. The manufacturer of this product actually recommends that it be used with parabens to provide fungicidal action.
Formaldehyde in the free state, as in formalin, is effective only for short periods of time. In addition, it is inactivated by protein.
Admixtures of methylchloroisothiazolinone and methylisothiazolinone (Kathon CG, a trademark of Rohm & Haas) are unstable in the presence of organic sulfur compounds, ingredients commonly used in personal care products. They react also with peroxide impurities present in materials such as amine oxides.
2-Bromo-2-nitropropane-1,3-diol (Lexgard Bronopol, a trademark of Inolex) has limited fungicidal activity and parabens are required to provide microbiological activity.
Alkyl parabens (e.g., methyl, ethyl and propyl) have limited bactericidal action. They are generally solubilized in oil since they are poorly soluble in water, leading to formulation difficulties for personal care and household products. They are often inactivated by commonly used materials such as gelatin, methyl cellulose, and polyethylene glycol.
The development of an effective synergistic combination, inexpensive in price and having a broad spectrum activity, has long been sought. For example, in U.S. Pat. No. 4,454,146, a preservative composition having two components (the first being benzoic acid, formaldehyde or a mixture of isothiazolinone and a second component containing compounds with condensed aromatic rings) has been suggested for preservative applications. In addition, U.S. Pat. No. 3,699,231 describes a synergistic mixture of sodium dimethyldithiocarbamate and formaldehyde for killing bacteria in drilling fluids; U.S. Pat. No. 3,929,561 comprises mixtures of isothiazolinones and bis(trichloromethyl) sulfones for inhibiting the growth of slime for industrial purposes; and U.S. Pat. No. 4,655,815 describes synergism between 2-bromo-2-bromomethylglutaronitril and a formaldehyde donor such as dimethyloldimethylhydantoin, hydroxyaminopropanol, hydroxyethylnitropropanediol, blends of hydroxymethyl azadioxabicyclooctane and hydroxymethylamino ethanol; chloroallyl triazoadamantine chloride, chloroallyl heximinium chloride and hexamethylene tetramine halo hydrocarbon quaternaries.
Unfortunately, the above compositions are not suitable for personal care and household products because of their unfavorable toxicity, particularly skin and eye irritation and/or incompatibility with commonly used ingredients.